The present invention relates to lamp sockets, and more particularly to a such a lamp socket having a metal socket fixed to the socket shell thereof to hold the lamp bulb in making an electric contact
Various decorative strings and Christmas tree light sets are well-known and intensively used western countries as well as most Asian countries during Christmas holidays. When installed, decorative strings and Christmas tree light sets are controlled to flash and to give different colors of light. In recent days, the requirement for a safety operation on decorative lighting devices has become more and more critical. UL and CSA define strict specifications on these products. The lamp socket for a decorative string or Christmas tree light set, as shown in FIG. 3, is generally comprised of an internally threaded plastic socket body 1 having a first contact metal plate 6 and a second contact metal plate 14 mounted on the inside. The socket body 1 has a wire groove 11 on the top end thereof for mounting the electric wire 5, and two slots 13 through which the top end of either contact metal plate projects. The contact metal plates 6 and 14 have each a beveled top edge projecting out of either slot 13 into the wire groove 11. When the electric wire 5 is placed in the wire groove 11, a plastic socket cap 3 is fastened to the socket body 1 to hold down the electric wire 5 causing the beveled top edges of the contact metal plates 6 and 14 pierced the insulator of either conductor of the electric wire 5 to make a respective electric contact. The first contact metal plate 6 has a curved bottom end transversely disposed inside the socket body 1 at the top and stopped between two ribs 15. When the base 41 of the lamp bulb 4 is threaded into the socket body 1, the tip and ring contacts of the lamp bulb 4 are respectively connected to the conductors of the electric wire 5 through the contact metal plates 6 and 14. This structure of lamp socket is functional however, it has drawbacks. The major drawback of this structure of lamp socket is that the socket body 1 may expand when hot, causing a gap produced between the base 41 of the lamp bulb 4 and the threaded inside wall of the socket body 1. Therefore, an electric shock may occur when one touches the lamp bulb 4.